To better phrase the question: Is the softlimit 10x or is it 100x because of the challenge? It scaled quite a bit faster then usual, maybe 10x faster.
the normal soft limit is +100%, the soft limit in the challenge is thugs +1000% or 10x. or at least I'm pretty sure it is. You can tell if you're at the soft limit or not by going to the stats and info screen and then looking at statistics and wave clears. It soft caps at 1000 wave clears, so if you have less than that it's a a ways to go yet to the soft cap